COVERAGE-DEPENDENT BONDING OF SB ON GAAS(110)

We performed total-energy pseudopotential calculations for a variety of structures for Sb adsorbed on the GaAs(110) surface. Sb coverages of theta = 1 and theta = 1/2 are considered. For theta = 1 we investigate five earlier proposed structures and find the epitaxial continued layer structure (ECLS) to be the lowest one in energy. The epitaxial on top structure (EOTS) which fits better to recent STM images is slightly higher in energy. The electronic structure and the changes of the ionization energies for these models are also discussed in the context of experimental results and give further evidence for the ECLS. Its structural parameters are found to be in excellent agreement both with LEED and XSW data. For a coverage of theta = 1/2 we find two equivalent minima in the total-energy surface corresponding to long-bridge positions in the 1 x 1 surface unit cell. Studies of 1 x 2 and 2 x 1 reconstructions for this coverage are performed as well. Together with the energetical results for theta = 1 they indicate the tendency of Sb to form two-dimensional clusters for low coverages as observed experimentally.